Umezawa et al. in application Ser. No. 297,458 now U.S. Pat. No. 4,416,899 filed Aug. 28, 1981 described the new antibiotic BMG162-aF2, its production by fermentation and isolation thereof from fermentation broths. The present inventors in application Ser. No. 375,950 now U.S. Pat. No. 4,430,346 (Japanese Application No. 69340/81 filed May 11, 1981) filed herewith describe a method for the synthesis of a new stereoisomer of BMG162-aF2 referred to therein as GHA-GS, and the antitumor properties of GHA-GS. The present invention provides an intermediate needed for that synthesis.